Column name from sql query in php

Question

I am trying to extract a column name from SQL database to use in a dropdown in HTML. I am then trying to insert PHP into the HTML dropdown to display column name.

I have used fetch array to get output from SQL using a variable from another drop down to pull the relevant SQL table. However i can't return the column name in PHP. All I get is the value using $row[2].

Is there an easy way to pull the column name (ie the non-numeric value in square brackets after the numerical value).

$query="SELECT * FROM ".($units_cat)."";

    if ($result = mysqli_query($link, $query)) {
        $row = mysqli_fetch_array($result);

        echo nl2br (" \n Query was successful \n");
        print_r($row);
        echo "<br>";
    } 

HTML

<option value="<?php $row[2]?>"
        <?php 
        if($_POST['units_from']==$row) 
            echo 'selected="selected"';?>
        >
<?php echo ($row[2])?>
</option>

OUTPUT FROM SQL QUERY

Array ( 
   [0] => 1 
        [id] => 1 
   [1] => Klbs 
        [from_value] => Klbs 
   [2] => 1.0000000000 
        [klbs] => 1.0000000000 
  [3] => 1000.0000000000 
        [pound] => 1000.0000000000 
  [4] => 0.4535923700 
        [ton] => 0.4535923700 
  [5] => 453.5923700000 
        [kg] => 453.5923700000 
  [6] => 224.8089424432 
        [newton] => 224.8089424432 
  [7] => 22.4808942443 
         [dn] => 22.4808942443 
  [8] => 0.2248089424 
         [kn] => 0.2248089424 
    )

Answer 1

I was able to do this by using DESCRIBE to output array of table data. Then create an array of the columns.

 $query2=("DESCRIBE ".mysqli_real_escape_string($link, $units_cat));

if ($result2 = mysqli_query($link, $query2)) {
    $table_desc = mysqli_fetch_all($result2);


#Create an array of column values   
    foreach($table_desc as $val) {  
        $col[]=$val[0]; 
    }

Then call the column values in the relevant dropdown.

 <option value="<?php echo($col[2]) ?>"<?php if($_POST['units_from']==($col[2])) echo 
 'selected="selected"';?>><?php echo($col[2]) ?></option>  

I had to white-list the tables that $units_cat was referencing as I believe you cannot prepare a table as you are unable to bind parameters to a table entry in PHP/SQL.

#Get tables list for whitelisting
$query3="Show tables";
$result3=mysqli_query($link,$query3);

if (!$result3) {
    echo "DB Error, could not list tables\n";
    echo 'MySQL Error: ' . mysqli_error();
    exit;
}

if ($result3=mysqli_query($link,$query3)){
    while($row=mysqli_fetch_row($result3)){

        $tables[]=$row[0];

    }
}       


#UNITS CAT WHITELIST CHECK  
if (in_array($units_cat,$tables)){

    echo nl2br (" \n Units Cat Table exists");

}else{

    echo "Table does not exist";
    mysqli_close($link);
    echo "<br>";
    die("non valid entry");
}

Answer 2

with mysql_fetch_array you can access each parameter individually $row['id']; $row['pound'];

However, storing the different values for a same variable (in kg, in tons , in...) in the database seems a bit unnecessary taking into account that you can save the space with a simple conversion using the metric unit. do your users need to input the weight in different units each time?